IEEE (Institute of Electrical and Electronics Engineers) 802.16 standard provides techniques and protocols to support a broadband wireless access. Standardization started from 1999 and IEEE 802.16-2001 was approved in 2001. It is based on a single carrier physical layer called ‘WirelessMAN-SC’. Later, besides the ‘WirelessMAN-SC’, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ were added to a physical layer in IEEE 802.16a standard approved in 2003. After the IEEE 802.16a standard was completed, a revised IEEE 802.16-2004 standard was approved in 2004. IEEE 802.16-2004/Cor1 (referred to as ‘IEEE 802.16e’, hereinafter) was finalized in the form of ‘corrigendum’ in 2005 in order to resolve and correct bugs and errors of the IEEE 802.16-2004 standard.
In order to receive and demodulate data of a wireless communication system, synchronization needs to be matched between a receiver and a transmitter. In particular, for a successful data transmission and reception in a mobile communication system in which a channel environment between a base station (BS) and a mobile station (MS) continuously changes, the synchronization between the BS and the MS should be matched through close signaling.
A communication channel between the BS and the MS includes a downlink (DL) channel proceeding from the BS to the MS and an uplink (UL) channel proceeding from the MS to the BS. In downlink, a plurality of MSs match downlink synchronization with data frames transmitted from the BS. In order for the MSs to match the synchronization, the BS may insert a preamble for synchronization into a portion of a frame. The MSs match synchronization for the downlink channels through the preamble. Alternatively, the BS may use a synchronization channel.
In uplink, each MS must transmit data through a time and/or frequency domain allocated to each MS in order to avoid an interference between the MSs and allow the BS to receive data. Thus, for the uplink synchronization, each MS needs to adjust synchronization through signaling between the BS and the MSs in consideration of the channel environment.
A signal exchanged between the MSs and the BS to match uplink synchronization in the IEEE 802.16 standard is called a ranging signal. A ranging process is a sequential process of adjusting transmission power through the process of exchanging the ranging signal between the MS and the BS and matching time/frequency synchronization. That is, the sequential process for obtaining uplink synchronization may be called the ranging process.
In an initial ranging, an accurate timing offset is obtained between the MS and the BS and transmission power is adjusted at the early stage. When power is turned on, the MS obtains downlink synchronization from a received downlink preamble signal. Subsequently, the MS performs initial ranging in order to adjust the uplink timing offset and the transmission power. Unlike the initial ranging, a periodic changing is a process of periodically tracking an uplink timing offset and a reception signal strength following the initial ranging.
In attempting a ranging process, a pre-set ranging code is used as a ranging signal.
Configuration of ranging channels in various frame structures will be described. First, technical terms will now be described.
In the description of the present invention, TCP is an OFDMA cyclic prefix duration, Tu is an available OFDMA symbol duration, and Ts (=TCP+Tu) is an OFDMA symbol duration including a CP (cyclic prefix).
A TTG, an RTG, an SSTTG, and an SSRTG are defined for a time division duplex (TDD) frame structure in 802.16e of IEEE P802.16 Rev2 standard.
1) RTG (Base Station (BS) Receive/Transmit Transition Gap)
The RTG is a gap between the last sample of an uplink burst and a first sample of a subsequent downlink burst at an antenna port of the BS having TDD transceiver. The RTG, namely, the gap, is an allowable time for the BS to switch from a reception mode to a transmission mode. During this gap, the BS simply ramps up a BS transmitter carrier and allows a transmission/reception antenna switch to actuate, without transmitting modulated data. The RTG is not applicable for frequency division duplex (FDD) systems.
2) TTG (Base Station (BS) Transmit/Receive Transition Gap)
The TTG is a gap between the last sample of the downlink (DL) burst and the first sample of the subsequent uplink (UL) burst at the antenna port of the BS having a time division duplex (TDD) transceiver. The TTG, namely, the gap, is an allowable time for the BS to switch from the transmission mode to the reception mode. During this gap, the BS simply ramps down a BS transmitter carrier and allows a transmission/reception antenna switch to actuate and a BS receiver to operate, without transmitting modulated data. The TTG is not applicable for frequency division duplex (FDD) systems.
3) SSRTG: (Subscriber Station Receive/Transmit Gap)
The SSRTG is a minimum receive-to-transmit turnaround gap. The SSRTG is the gap measured from the time of the last sample of the received burst to the first sample of the transmitted burst at the antenna port of the SS.
4) SSTTG (Subscriber Station Transmit/Receive Gap)
The SSTTG is a minimum transmit-to-receive turnaround gap. The STTG is the gap measured from the time of the last sample of the transmitted burst to the first sample of the received burst at the antenna port of the SS).
Meanwhile, the length of the TTG and the RTG is defined to be at least 5 μs in the 802.16e standard, and the BS informs the MSs about that through DCD channel encoding. Here, the DCD channel encoding is as shown in Table 1.
TABLE 1TypeName(1 byte)LengthValue(variable length)PHY scopeDownlink_Burst_Profile1—May appear more thanAllonce(see 6.3.2.3.1). Thelength is the number of bytesin the overall object,including embedded TLVitems.BS EIRP22Signed in units of 1 dBmAllFrame34The number of PSs containedSCdurationin a Burst FDD or TDDframe. Required only forframed DLs.PHY Type41The PHY Type to be used.SCPower adjustment510 = Preserve PeakSCrulePower1 = Preserve Mean PowerDescribes the power adjustmentrule whenperforming a transition fromone burst profile to another.Channel Nr61DL channel number asOFDM,defined in 8.5. Used forOFDMAlicense-exempt operationonly.TTG72 for TDD, 4TTG (in PSs). Note: for H-OFDMAFOR H-FDDFDD, the first set of 2 bytescorresponds to H-FDD Group1, While the second set of 2bytes corresponds to H-FDDGroup 2RTG81 for TDD, 2RTG (in PSs). Note: for H-OFDMAFOR H-FDDFDD, the first byte correspondsto H-FDD Group1, While the second byte correspondsto H-FDD Group 2.
Also, the length of the SSTTG and the SSRTG may be transmitted between the BS and the MS through SBC-REQ/RSP management message encoding in the 802.16e standard. However, the message is generated between the BS and the MS for a capability negotiation during an initial network entry procedure, and the length cannot be known in the state that the MS initially transmits a ranging code to the BS.
TABLE 2TypeLengthValueScope22Bits: 0-7: SSTTG(μs) Bits: 8-15:SBC-REQSSRTG(μs)Allowed(see 6, 3, 2, 3, 23)values: OFDM mode: TDDSBC-RSPand H-FDD 0 . . . 100. Other(see 6, 3, 2, 3, 24)modes: TDD: 0 . . . 50; H-FDD: 0 . . . 100.
In order to guarantee a minimum performance of the MS from a WiMAX Forum Mobile System Profile Release 1.0 (Revision 1.4.0), the SSRTG and the SSTTG may have a time length of 50 μs, while the TTG and the RTG may have different values according to system bandwidth as shown in Table 3 below:
TABLE 3TTGRTGBW [MHz]nFs [MHz]PS [us][PS][us][PS][us]101.1211.20.357143296105.7143168608.751.142857100.421887.218674.471.14285780.53761881206051.125.60.714286148105.714384603.51.142857411881886060
In Table 3, the BW indicates a system bandwidth, ‘n’ is a sampling factor and 8/7 or 28/25 is used depending on a BW. Fs is a sampling frequency, which is defined as Fs=floor(n·BW/8000)?8000. A PS is a physical slot, which is defined as PS=4/Fs. The values of TTG and RTG are indicated by PS and us.
FIG. 1 illustrates a type-1 frame structure in the TDD duplex mode. In FIG. 1, TCP in the 802.16m standard is TCP=1/8·Tu. In FIG. 1, a superframe having a 20 ms duration includes four frames. Each frame has 5 ms and includes eight subframes. The subframes are divided into a type-1 subframe (or a regular subframe) and a type-1 short subframe (or an irregular subframe). The type-1 subframe includes six OFDMA symbols of 0.617 ms. The type-1 short subframe occupies the same time as that of the type-1 subframe, but is different from the type-1 subframe in that the last OFDMA symbol of the type-1 short subframe is an idle symbol. The idle symbol is not used for a transmission. While changing from DL to UL, there is an idle time of 102.857 us, and an idle time of 62.86 us exists at a switching point at which US is changed to DL.
FIG. 2 illustrates the type-1 frame structure in the FDD duplex mode. In FIG. 2, TCP in the 802.16m standard is TCP=1/8·Tu. In FIG. 2, a superframe having a 20 ms duration includes four frames. Each frame has 5 ms and includes eight subframes, and there exists an idle time of 62.86 us. A subframe includes six OFDM symbols of 0.617 ms.
FIG. 3 illustrates a frame structure in a TDD and FDD duplex mode having a TCP=1/8·Tu in the 802.16m standard. In FIG. 3, each frame has 5 ms and includes eight subframes. The subframes are divided into a type-1 subframe and a type-2 subframe. Namely, the type-1 subframe includes six OFDM symbols of 0.583 ms, and the type-2 subframe includes seven OFDM symbols of 0.680 ms. In case of the TDD duplex mode, there exists a transmitter transition gap (TTG) while DL is changed to UL and there exists a receiver transition gap (RTG) while UL is changed to DL. In case of the FDD duplex mode, there exists an idle time at the end of each frame.